private byte readImageDescriptor(InputStream is) throws Exception {
int nindex = 0;
byte ides[] = new byte[9];
IOUtils.readFully(is, ides, 0, 9);
image_x = (ides[nindex++] & 0xff) | ((ides[nindex++] & 0xff) << 8);
image_y = (ides[nindex++] & 0xff) | ((ides[nindex++] & 0xff) << 8);
width = (ides[nindex++] & 0xff) | ((ides[nindex++] & 0xff) << 8);
height = (ides[nindex++] & 0xff) | ((ides[nindex++] & 0xff) << 8);
return ides[nindex++];
}
private void readLocalPalette(InputStream is, int num_of_color) throws Exception {
int index1 = 0;
int bytes2read = num_of_color * 3;
byte brgb[] = new byte[bytes2read];
IOUtils.readFully(is, brgb, 0, bytes2read);
rgbColorPalette = new int[num_of_color];
for (int i = 0; i < num_of_color; i++)
rgbColorPalette[i] =
((255 << 24)
| ((brgb[index1++] & 0xff) << 16)
| ((brgb[index1++] & 0xff) << 8)
| (brgb[index1++] & 0xff));
}
void readHeader(InputStream is) throws Exception {
int nindex = 0;
byte bhdr[] = new byte[13];
IOUtils.readFully(is, bhdr, 0, 13);
for (int i = 0; i < 3; i++) signature[i] = bhdr[nindex++];
for (int i = 0; i < 3; i++) version[i] = bhdr[nindex++];
screen_width = ((bhdr[nindex++] & 0xff) | ((bhdr[nindex++] & 0xff) << 8));
screen_height = ((bhdr[nindex++] & 0xff) | ((bhdr[nindex++] & 0xff) << 8));
flags = bhdr[nindex++];
bgcolor = bhdr[nindex++];
aspectRatio = bhdr[nindex++];
// The end
}
private byte[] readFrame(InputStream is) throws Exception {
// One time read of global scope data
if (gifHeader == null) {
if (!readGlobalScopeData(is)) return null;
}
resetFrameParameters();
int image_separator = 0;
do {
image_separator = is.read();
if (image_separator == -1 || image_separator == 0x3b) { // End of stream
LOGGER.info("End of stream!");
return null;
}
if (image_separator == 0x21) // (!) Extension Block
{
int func = is.read();
int len = is.read();
if (func
== 0xf9) { // Graphic Control Label - identifies the current block as a Graphic Control
// Extension
int packedFields = is.read();
// Determine the disposal method
disposalMethod = ((packedFields & 0x1c) >> 2);
LOGGER.info(
"Disposal method: {}",
(disposalMethod == 0)
? "UNSPECIFIED"
: (disposalMethod == 1)
? "LEAVE_AS_IS"
: (disposalMethod == 2)
? "RESTORE_TO_BACKGROUND"
: (disposalMethod == 3) ? "RESTORE_TO_PREVIOUS" : "TO_BE_DEFINED");
userInputFlag = ((packedFields & 0x02) >> 1);
LOGGER.info("User input flag: {}", (userInputFlag == 0) ? "INPUT_NONE" : "INPUT_SET");
delay = IOUtils.readUnsignedShort(is);
LOGGER.info("Delay: {} miliseconds", delay * 10);
// Read transparent color index
int transparent_color_index = is.read();
// Check for transparent color flag
if ((packedFields & 0x01) == 0x01) {
transparencyFlag = GIFFrame.TRANSPARENCY_INDEX_SET;
LOGGER.info("transparent gif...");
transparent_color = transparent_color_index;
}
len = is.read(); // len=0, block terminator!
}
// GIF87a specification mentions the repetition of multiple length
// blocks while GIF89a gives no specific description. For safety, here
// a while loop is used to check for block terminator!
while (len != 0) {
IOUtils.skipFully(is, len);
len = is.read(); // len=0, block terminator!
}
}
} while (image_separator != 0x2c); // ","
byte flags2 = readImageDescriptor(is);
boolean hasLocalColorMap = false;
if ((flags2 & 0x80) == 0x80) {
hasLocalColorMap = true;
// A local color map is present
LOGGER.info("local color map is present");
bitsPerPixel = (flags2 & 0x07) + 1;
colorsUsed = (1 << bitsPerPixel);
LOGGER.info("{} color image", colorsUsed);
readLocalPalette(is, colorsUsed);
}
if (!hasLocalColorMap) rgbColorPalette = globalColorPalette;
if (transparencyFlag == GIFFrame.TRANSPARENCY_INDEX_SET && transparent_color < colorsUsed)
rgbColorPalette[transparent_color] &= 0x00ffffff;
if ((flags2 & 0x40) == 0x40) {
LOGGER.info("Interlaced gif image!");
return decodeLZWInterLaced(is);
}
return decodeLZW(is);
}